Deadman control

ABSTRACT

A &#39;&#39;&#39;&#39;deadman&#39;&#39;&#39;&#39; control for engine driven power tool including an engine grounding circuit having serially arranged first and second switches; the first switch being normally closed, but assuming an open condition upon gripping of a tool control handle by a tool operator, and the second switch being normally open for engine idle speeds, but assuming a closed condition under normal engine operator speeds.

I United States Patent 1 1 1 1 3,849,620 Melisz Nov. 19, 1974 DEADMAN CONTROL 3,229,452 1/1966 Hasenbank 56/F1G. 15 x 3,731,471 /1973 Bening 56/D1G. X lnvenm Mel'szr 3,736,915 6/1973 Dickensheets et al. 123/198 DC [73] Assignee: Lisk Savory Corporation, Buffalo,

NY. Primary Examiner-Robert K. Schaefer Assistant Examiner-William J. Smith [22] Flled' June 1973 Attorney, Agent, or Firm-Bean & Bean [21] Appl. No.: 369,708

[57] ABSTRACT 2% 8 zoo/157 ii fi'i gg A deadman control for engine driven power tool in- 307/94 f ZOO/1ST eluding an engine grounding circuit having serially arl 0 b 1 5 10 f ranged first and second switches; the first switch being 317/ R, 1 F -1 normally closed lgut assuming an open condition upon /1 gripping of a tool control handle by a tool operator, and the second switch being normally open for engine [56] References cued idle speeds, but assuming a closed condition under UNITED STATES PATENTS normal engine operator speeds. 2,873,811 2/1959 Uffert el al. /99 3,141,944 7/1964 DeVoe 200/157 3 Clam, 4 Draw sum 20$ 2 PATENTE 1m 1 9 1914 DEADMAN CONTROL BACKGROUND OF THE INVENTION Prior deadman controls for internal combustion engine driven power tools, have utilized the principle that an engine will automatically stop, when its ignition system is shorted or connected to ground.

In this type of deadman control, it is quite common to provide a switch in association with a tool operating control handle, such that when an operator releases his grip on the handle the switch automatically closes to connect the engine magneto or spark plug to ground. As by way of specific example, reference may be made to U.S. Pat. No. 3,141,944 and 3,228,177.

SUMMARY OF THE INVENTION The present invention is directed towards an improved deadman control for internal combustion engine driven tools.

The deadman control of the present invention features an engine grounding circuit having serially arranged first and second switches associated with the tool handle and engine throttle control respectively. The first or handle associated switch is a closed switch adapted to be opened in response to gripping of the handle, whereas the second or throttle associated switch is an open switch adapted to be closed in response to movement of the throttle away from an engine idle position. When both switches are closed, the grounding circuit is completed and the engine automatically stops.

Thus, with the present deadman control, an operator may start up the engine without gripping the handle, if the throttle is in an engine idle position.

To operate the tool, the operator first grips the handle to effect opening of the first switch and then moves the throttle into a normal operating speed or run condition. Since movement of the throttle from its idle position results in the closing of the second switch, subsequent release of the handle for any reason, will result in automatic completion of the grounding circuit and stopping of the engine.

Nonnally, when an operator wishes to stop tool operation, he will first return the throttle to idle condition. Thereafter, he may leave the tool momentarily unattended with the engine idling. Alternatively, he can stop the engine by merely moving the throttle from its idle condition to complete the grounding circuit.

DRAWINGS The nature and mode of operation of the present invention will now be more fully described in the following detailed description taken with the accompanying drawings wherein:

FIG. 1 is a perspective view showing an engine operated tool having the control of the present invention incorporated thereon;

FIG. 2 is an enlarged fragmentary view of a portion of the handle of the tool illustrated in FIG. 1;

FIG. 3 is a side elevational view of the portion of the handle illustrated in FIG. 2; and

FIG. 4 is a diagrammatic view of the grounding circuit for the ignition system of the tool.

DETAILED DESCRIPTION For purposes of illustration, the deadman control of the present invention will be described as being incorporated in a power trowel 10, which isshow-n in FIG. 1 as generally including an internal combustion engine 12 mounted on a suitable main frame 14 for the purpose of effecting driven rotations of a plurality of concrete surface finishing blades or plates 16. Trowel 10 is equipped with a main frame attached, upwardly and outwardly extending handle frame 18, which serves to define a pair of handles 20a and 20b to be gripped by the hands of an operator for the purpose of guiding and/or otherwise manipulating trowel 10.

A housing 22 may be fixed to handle frame 18 adjacent the junctures of handles 20a and 20b in order to provide a convenient mounting station for an engine speed control throttle mechanism 24 and a mechanism 26 for controlling the vertical positioning of blades 16. While throttle mechanism 24 may be of any desired construction, it is shown for purposes of illustration in FIGS. 2 and 3 as including a throttle lever 28, which is pivotally secured, as by pin shaft 30, to a housing mounted bracket 32 for movement between the engine idle and engine run positions illustrated for example in full and phantom line, respectively, in FIG. 3. Throttle lever 28 may be suitably connected to the carburator of engine 12 as by a push-pull cable 34. It will be understood that the term engine run, as used herein is meant to include any engine speed condition at which the trowel is normally operated other than essentially idle speed.

Also, as is conventional with trowels of the type thus far described, engine 12 is provided with a suitable ignition system including a source of electricity, such as a magneto, not shown, and a spark plug, also not shown, which are connected by a suitable conductor, such as that designated as 36 only in FIG. 1. It will be understood that this type of ignition system is commonly provided with a terminal designated as 38 only in FIG. 4, which may be selectively connected to ground, as for instance by an electrical circuit including an ON-OFF switch, in order to disable the ignition system with the result that engine 12 will automatically stop.

In accordance with the present invention, an improved grounding circuit, which is designated generally as 40 in FIG. 4, is employed to selectively connect terminal 38 to ground, such as may be defined by a handle frame affixed bolt 42. Circuit 40 includes serially arranged first and second switches 44 and 46, respectively, which when simultaneously closed serve to ground or short the ignition system of motor 12.

Now referring to FIGS. 2 and 4, it will be seen that first switch 44 is a push-button type of switch in that it generally includes switch casing 48, which is suitably afiixed to housing 22; and an operating plunger 50 mounted within casing 48 to extend rearwardly through housing 22 for reciprocating movement between a normally extended switch closed position and a retracted or depressed switch open position. As is conventional with switches of this type, a suitable spring 52, which is shown only in FIG. 4, is arranged within casing 48 for the purpose of normally biasing plunger 50 towards and into its extended position.

By again referring to FIG. 2, it will be understood that plunger 50 is adapted to be forced into its retracted position by engagement with a member in the form of a handle lever 54, whenever an operator grips the handle with which the handle lever is associated. Specifically, handle lever 54 is shown as beingassociated with handle 20a and as' being secured thereto intermediate its ends by means of a pivot pin or bolt 56 for pivotal movement between first and second positions shown in full and phantom line, respectively, in FIG. 2. Handle lever 54 may be considered as having a first end or operator gripping portion 54a, which is of U-shaped or curved cross-sectional configuration so as to generally conform to the forward surface of its associated handle a when the handle lever is disposed in its second condition; and a second end or first switch operating portion 54b, which is preferably of a generally L-shaped cross-sectional configuration so as to define a depending flange 54b arranged for engagement with the outer or rearwardly extending end of plunger 50.

Preferably, a handle engaging spring, such as a leaf spring 58, is provided for the purpose of normally biasing handle lever 54 into its first position. Alternatively, if the spring 52 of first switch 44 is sufficiently strong, spring 58 may be dispensed with and the switch spring employed to normally bias the handle lever into its first position, due to engagement of the outer end of plunger 50 with flange 54b. In either case, when the handle lever is disposed in its first position, end portion 54a is disposed sufficiently close to the forwardly facing surface of its associated handle 20a, such that when an operator attempts to grip or grasp handle 20a, his fingers will automatically engage or grip end portion 54a and thereby serve to move same towards the handle, whereby to move the handle lever from its first into its second position and effect opening of switch 44. Thus, first switch 44 may be considered or characterized as being responsive to the gripping and releasing of handle 20a for assuming grounding circuit open and closed conditons, respectively.

By referring to FIGS. 2 and 4, it will be seen that second switch 46 includes a casing 60, which is suitably fixed to a lower surface of housing 22 adjacent throttle mechanism 24; and an operating toggle or lever 62 arranged for engagement with throttle lever 28. Toggle 62 is mounted on casing 60 for pivotal movement between forwardly disposed switch open and rearwardly disposed switch closed positions, shown in full and phantom line, respectively, in FIG. 2. As is conventional with switches of this type, a suitable spring 64, which is shown only in FIG. 4, is arranged within casing 60 for the purpose of normally biasing toggle 62 towards and into its rearwardly disposed switch closed position. Thus, in the illustrated construction, when throttle lever 28 is disposed in an engine idle position, toggle 62 is maintained thereby in its forwardly disposed switch open position against the bias of spring 64, and when the toggle lever is moved towards engine run position spring 64 automatically moves toggle 62 rearwardly into a switch open condition. Thus, second switch 46 may be considered or generally characterized as being responsive to the condition of the throttle mechanism 24 in that it assumes circuit open and closed conditions for engine idle and engine run conditions, respectively.

A power trowel fitted with the deadman" control of the present invention may be operated in the following manner. When it is desired to start engine 12, an operator would normally first position throttle lever 28 in engine idle position for the purpose of opening switch 46 to break grounding circuit 40, and then start the engine in a normal manner, such as by pulling on the starter cord, not shown. Alternatively, engine 12 may be started with the throttle lever in engine run condition,

matically close to complete circuit 40 with the result that engine 12 will automatically stop.

Normally, when an operator wishes to stop trowelling, he will first return the throttle lever to idle position. He may then leave the trowel momentarily unattended with the engine idling. Alternatively, he can stop the engine after he has released his grip on handle 20a by merely moving the throttle lever from its idle position in order to complete the grounding circuit.

While the deadman control of the present invention has been specifically described with respect to its use in a power trowel, it will of course be understood that the present deadman control is of more general utility in that it may be incorporated in any engine driven tool or device, wherein it is desirable to automatically stop tool operation by grounding the engine whenever a tool operator releases the tool handle or other mechanism indicative of the control presence of the operator.

Further, it will be understood that the present deadman control is not limited to the use of a pushbutton type first switch and a toggle second switch, wherein springs are employed to bias the switches into closed condition. In this respect, it is specifically contemplated that the first and second switches may be of any conventional construction and may have their operators positively coupled with the handle and throttle levers for ON and OFF movements in order to negate the need for providing the switches with internal springs.

I claim:

1. A power trowel comprising in combination:

a trowel drive engine mounted on a frame;

handle means fixed to extend from said frame and including a pair of handles to be gripped by an operator for manipulating said trowel;

a handle lever mounted on one of said handles for movement between first and second positions;

spring means for normally biasing said handle lever into said first position, said handle lever being manually movable into said second position against the bias of said spring means incident to the gripping of said one handle by said operator;

a speed control throttle for said engine including a throttle lever carried by said handle means for movement between engine idle and engine run positions; and

first and second switches, said first switch having a casing fixed to said handle means adjacent said one handle, an operator mounted by its associated casing for movement between switch closed condition and a switch open condition and switch spring means for normally biasing its associated operator into switch closed condition, said handle lever when in said second position having one end thereof arranged to lie closely adjacent said one handle and having another end thereof arranged in engagement with said operator of said first switch for releasably maintaining same in its switch open condition against the bias of its associated spring means, and said second switch having a casing fixed to said handle means adjacent said throttle lever, an operator mounted by its associated casing for movement between a switch closed condition and a switch open condition and switch spring means for normally biasing its associated operator into switch closed condition, said throttle lever when in engine idle position engaging said operator of said second switch for releasably maintaining same in its switch open condition against the bias of its associated spring means, said first and second switches being serially arranged within a circuit for connecting said engine to ground when the operaand open conditions. 

1. A power trowel comprising in combination: a trowel drive engine mounted on a frame; handle means fixed to extend from said frame and including a pair of handles to be gripped by an operator for manipulating said trowel; a handle lever mounted on one of said handles for movement between first and second positions; spring means for normally biasing said handle lever into said first position, said handle lever being manually movable into said second position against the bias of said spring means incident to the gripping of said one handle by said operator; a speed control throttle for said engine including a throttle lever carried by said handle means for movement between engine idle and engine run positions; and first and second switches, said first switch having a casing fixed to said handle means adjacent said one handle, an operator mounted by its associated casing for movement between switch closed condition and a switch open condition and switch spring means for normally biasing its associated operator into switch closed condition, said handle lever when in said second position having one end thereof arranged to lie closely adjacent said one handle and having another end thereof arranged in engagement with said operator of said first switch for releasably maintaining same in its switch open condition against the bias of its associated spring means, and said second switch having a casing fixed to said handle means adjacent said throttle lever, an operator mounted by its associated casing for movement between a switch closed condition and a switch open condition and switch spring means for normally biasing its associated operator into switch closed condition, said throttle lever when in engine idle position engaging said operator of said second switch for releasably maintaining same in its switch open condition against the bias of its associated spring means, said first and second switches being serially arranged within a circuit for connecting said engine to ground when the operator of both of said switches is in its switch closed condition whereby to stop said engine.
 2. A power trowel according to claim 1, wherein said handle lever is mounted for pivotal movement, and said operator of said first switch is mounted for reciprocating movement between switch closed and open conditions.
 3. A power trowel according to claim 1, wherein said throttle lever is mounted for pivotal movement between engine idle and engine run positions, and said second switch is a toggle switch having its operator mounted for pivotal movement between switch Closed and open conditions. 